ABSTRACT
Acknowledgments ................................................................................................ 223
References............................................................................................................. 223
Modulation of cytoplasmic free-calcium concentration ([Ca2þ]i) is a ubiquitous signaling system involved in the regulation of numerous processes, including transe-
pithelial transport, learning and memory, muscle contraction, synaptic transmission,
secretion, motility, membrane trafficking, excitability, gene expression, and cell
division. Activation of phospholipases Cb and Cg (PLC) by ligand interaction with G-protein-or tyrosine kinase-linked receptors, respectively, results in hydrolysis
of phosphatidylinositol-4,5-bisphosphate, generating inositol 1,4,5-trisphosphate
(InsP3). InsP3 binds to its receptor (InsP3R), a ligand-gated Ca 2þ release channel
[1, 2] localized in the endoplasmic reticulum (ER) [3]. Analyses of InsP3-mediated
[Ca2þ]i signals in single cells have revealed them to be unexpectedly complex. In the temporal domain, this complexity is manifested as repetitive spikes or oscillations,
with frequencies often tuned to levels of stimulation, suggesting that [Ca2þ]i signals may be transduced by frequency encoding as well as amplitude. In the spatial domain,
[Ca2þ]i signals may initiate at specific locations and remain highly localized or propagate as waves [4-7]. Thus, InsP3-mediated [Ca
2þ]i signals are often organized to provide different signals to discrete parts of the cell.
